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Journal of Organometallic Chemistry 745-746 (2013) 18e24

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Journal of Organometallic Chemistry

journal homepage: www.elsevier .com/locate/ jorganchem

Investigation of catalytic activity of new Co(II) phthalocyaninecomplexes in cyclohexene oxidation using different type of oxidants

Ayse Aktas a, Ece Tu�gba Saka a,*, Zekeriya Bıyıklıo�glu a, _Irfan Acar b, Halit Kantekin a

aDepartment of Chemistry, Karadeniz Technical University, 61080, Trabzon, TurkeybDepartment of Energy System Engineering, Faculty of Of Technology, Karadeniz Technical University, 61830, Of, Trabzon, Turkey

a r t i c l e i n f o

Article history:Received 15 May 2013Received in revised form21 June 2013Accepted 5 July 2013

Keywords:PhthalocyanineCobalt(II)Cyclohexene oxidationOxidantm-Chloroperoxybenzoic acid

* Corresponding author. Tel.: þ90 462 377 3666; faE-mail address: ece_t_saka@hotmail.com (E.T. Sak

0022-328X/$ e see front matter � 2013 Elsevier B.V.http://dx.doi.org/10.1016/j.jorganchem.2013.07.013

a b s t r a c t

In this work, the new phthalonitrile derivatives 4, 5 bearing 1,3-bis(naphthalen-1-yloxy)propan-2-ol and1,3-bis(naphthalen-2-yloxy)propan-2-ol, cobalt phthalocyanine complexes have been synthesized. Thenew cobalt phthalocyanines have been prepared by cyclotetramerization of phthalonitrile derivatives 4, 5in the presence of the corresponding CoCl2 salt in DMAE by using a microwave oven. The new com-pounds have been characterized by IR, 1H NMR, 13C NMR and MS spectral data. The new complexes havebeen tested as a catalyst for the oxidation of cyclohexene with different oxidants, such as tert-butylhy-droperoxide (TBHP), m-chloroperoxybenzoic acid (m-CPBA) and hydrogen peroxide (H2O2), in DMF. m-CPBA is also found as the most successful oxidant in the other oxygen sources. In this sense, the sub-strate/catalyst ratio, the influence of temperature, oxidant/cat ratio and type of oxidant have beenstudied. It is observed three oxidation products. First one is 2-cyclohexene-1-ol as dominant product andthe others are 2-cyclohexene-1-one and cyclohexene oxide as minor product.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

The industrial and environmental preoccupations meet on theircommon need for more efficient and cheaper catalysts. These high-tech catalysts are required for a more effective degradation ofpollutants, which is one of their two main uses, or for high scalesynthetic purposes. Oxidation of different type of molecules such asalkyl aromatics, alkenes and alcohols are of particular importanceas it lead to small molecules used as starting products for morecomplex syntheses in fine chemicals production (pharmaceutics,cosmetics, polimerization monomers). As the transformed func-tions can lead to different products, the selectivity of the catalyst isessential to the overall catalytic system’s efficiency [1].

Bioinspired heme-like catalysts were developed for syntheticpurposes as their natural models are active oxidant catalysts, highlyselective and performing. Porphyrin’s structure common to theseenzymes was therefore used by synthetic chemists aiming atdeveloping new catalytic structures. Phthalocyanines, tetraaza-benzoporphyrins analogs of porphyrins, after having been used assimple dyes and pigments, rise interests since a few decades astheir multi functional structure (large delocalized aromatic system,metallation, flexibility on a substitution pattern point of view) as

x: þ90 462 325 3196.a).

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well as their exceptional stability in time and extreme conditions(temperature, pH, etc.). Furthermore, they are intensively used ashomogenoushomogenous and heterogenous catalyst, liquid crystal,electro-and photo-chemical sensor, photoconductive materials,batteries and fuel supplies, photosensitizier in photodynamictherapy agent [2e7]. They are known to possess better catalyticproperties than the prophyrins, especially thanks to their superiorstability in oxidation conditions.

The higher oxidation states of the central transitionmetal ions aremore readily accessible in the porphyrin series than in the phthalo-cyanine series [8]. In other words, phthalocyanine ligand tends tostabilize the lower oxidation states of metal compared to porphyrinone. This implies that high oxidation states metallophthalocyaninesshould be stronger oxidizing agents than their porphyrin analogs inthe same oxidation state. In porphyrin series the kind of the cleavageof OeO bond is determined by the structures of porphyrin ligand andperoxide and the presence of axial ligand, which favors a heterolyticOeObondcleavage [9]. In addition, cobalt phthalocyanine complexesare also used as oxidation catalyst for selective oxidation of olefines[10]. It is found that Co(II) phthalocyanines can transfer oxygen fromvarious oxygen donors to alkanes, alkenes, phenols and thiols inthe several studies [11e22]. Condensed aromatic compounds con-taining naphthalene derivatives are effective functional groups inphotoemission studies [23,24]. Thus, in this paper we have aimed tosynthesize a new class of cobalt phthalocyanines bearing 4-{2-(1-Naphthyloxy)-1-[(1-naphthyloxy)methyl]ethoxy}, 4-{2-(1-Naphthy

A. Aktas et al. / Journal of Organometallic Chemistry 745-746 (2013) 18e24 19

loxy)-1-[(2-naphthyloxy)methyl]ethoxy} groups on the substituents. Additionally, the present paper also has reported on the appli-cation of phthalocyanine-based homogenous catalysts in the oxida-tion of cyclohexene.We have investigated the oxidationprocesswiththe purpose of developing product selectivity and increasing therange of products. Co(II) phthalocyanine complexes have beencompared as best catalysts for the oxidation.

2. Experimental

All reactions were carried out under a dry nitrogen atmosphereusing standard Schlenk techniques. All chemicals, solvents andreagent were of reagent grade quality and were used as purchasedfrom commercial sources. All solvents were dried and purified asdescribed by a reported procedure [25]. 1,3-Bis(naphthalen-1-yloxy)propan-2-ol 1 and 1,3-bis(naphthalen-2-yloxy)propan-2-ol2were synthesized according to the literature, respectively [26,27].

2.1. Synthesis

2.1.1. 4-{2-(1-Naphthyloxy)-1-[(1-naphthyloxy)methyl]ethoxy}phthalonitrile (4)

4-Nitrophthalonitrile 3 (0.6 g, 3.5 � 10�3 mol) was dissolved in0.03 L dry DMF under N2 atmosphere, and of 1,3-bis(naphthalen-1-yloxy)propan-2-ol 1 (1.2 g, 3.5 � 10�3 mol) was added to themixture. After stirring for 30 min at 60 �C, finely ground anhydrousK2CO3 (1.45 g, 10.5 � 10�3 mol) was added portion wise within 2 h.The reactionmixturewas stirred under N2 at 60 �C for 4 days. At theend of this time, the reaction mixture was poured into ice-waterand stirred at room temperature for 1 h to yield a crude product.The mixture was filtered and dried in vacuum over P2O5 for 4 h andrecrystallized from ethanol to give light yellow crystalline powder.Yield: 0.6 g (35%). mp: 63e67 �C. IR (KBr pellet), nmax/cm�1: 3055e3019 (Ar-H), 2931e2879 (Aliph. CeH), 2232 (C<ce:glyphname¼"tbnd"/>N), 1728, 1669, 1600, 1575, 1505, 1400, 1349, 1157,1143, 1000, 1021, 1024, 973, 873, 769, 667, 571, 524. 1H NMR.(CDCl3), (d: ppm): 8.08 (d, 2H, Ar-H), 7.84 (d, 2H, Ar-H), 7.66 (m,11H,Ar-H), 6.89 (d, 2H, Ar-H), 5.41 (t, 1H, OeCH), 4.61 (m, 4H, OeCH2).13C NMR. (CDCl3), (d: ppm): 162.48, 155.32, 136.74, 134.58, 127.88,127.08, 126.68, 126.12, 124.48, 123.76, 121.22, 117.87, 116.52, 115.91,115.36, 112.57, 107.48, 106.05, 79.85, 67.30. MS (ESI), m/z: 470 [M]þ.

2.1.2. 4-{2-(2-Naphthyloxy)-1-[(2-naphthyloxy)methyl]ethoxy}phthalonitrile (5)

Synthesized similarly to 4 from 2. Yield: 0.3 g (15%). IR (KBrpellet), nmax/cm�1: 3054e3017 (Ar-H), 2928e2877 (Aliph. CeH),2231 (C<ce:glyph name¼"tbnd"/>N), 1728, 1628, 1596, 1508, 1462,1317, 1253, 1240, 1178, 1157, 1102, 1020, 972, 874, 836, 792, 771, 667,570. 1H NMR. (CDCl3), (d: ppm): 7.77 (m, 6H, Ar-H), 7.53e7.18 (m,11H, Ar-H), 5.27 (m, 1H, OeCH), 4.53 (m, 4H, OeCH2). 13C NMR.(CDCl3), (d: ppm): 162.56, 156.04, 135.51, 134.50, 130.11, 129.57,127.98, 126.99, 124.47, 121.40, 120.90, 118.61, 117.73, 116.38, 115.61,112.56, 107.13, 104.72, 79.45, 67.39. MS (ESI), m/z: 470 [M]þ.

2.1.3. Cobalt(II) phthalocyanine (6)Amixture of compound 4 (300 mg, 0.64 mmol), anhydrous CoCl

(41.5 mg, 0.32 mmol) and dry DMAE (3 mL) was irradiated in amicrowave oven at 175 �C 350 W for 7 min. Then dark greenproduct was filtered and solid raw accomplished by column chro-matography which is placed aluminum oxide (Al2O3) usingCHCl3:CH3OH (5:1) as solvent system. The yield: 210 mg, (68%) mp:>300 �C. IR (KBr tablet) nmax/cm�1: 3053 (Ar-H), 2953e2852 (Aliph.CeH), 1722, 1595, 1579, 1508, 1460, 1385, 1267, 1238, 1178, 1156,1102, 1020, 967, 790, 770, 570. UVevis (THF): lmax, nm (log 3): 671(4.59), 605 (4.02), 320 (4.67). MALDI-TOF-MS: m/z: 1941 [M þ H]þ.

2.1.4. Cobalt(II) phthalocyanine (7)Synthesized similarly to 6 from 5. Yield: 92 mg (40%). mp:

>300 �C. IR (KBr tablet) nmax/cm�1: 3058 (Ar-H), 2957e2855(Aliph.CeH), 1727, 1628, 1599, 1510, 1463, 1390, 1254, 1217, 1182, 1120,1071, 965, 837, 750, 623, 471. UVeVis (THF): lmax, nm (log 3): 669(4.32), 604 (3.74), 328 (4.27). MALDI-TOF-MS: m/z: 1941 [M þ H]þ.

2.2. Measurements

FT-IR spectra were obtained on a PerkineElmer 1600 FT-IRspectrophotometer with the samples prepared as KBr pellets. Op-tical spectra in the UVevisible regionwere recordedwith a PerkineElmer Lambda 25 spectrophotometer. 1H and 13C NMR spectrawererecorded on a Varian Mercury 200 MHz spectrometer in CDCl3, andchemical shifts were reported (d) relative toMe4Si as internalstandard. Mass spectra were measured on a Micromass Quatro LC/ULTIMA LCeMS/MS spectrometer. MALDI-MS of complexes wasobtained in dihydroxybenzoic acid as MALDI matrix using nitrogenlaser accumulating 50 laser shots using Bruker Microflex LT MALDI-TOF mass spectrometer. Melting points were measured on anelectrothermal apparatus. A domestic microwave ovenwas used forall syntheses of phthalocyanines.

2.3. General procedure for the oxidation of cyclohexene

All reactions were performed in a thermostated Schlenk vesselequipped with a condenser and stirrer. The solution of cyclohexeneand catalyst in solvent were purified with bubbling nitrogen gas toremove the oxygen. A mixture of cyclohexene (0.78 � 10�3 mol),catalysts (2.57 � 10�6 mol) and solvent mixture (0.01 L) werestirred in a Schlenk vessel for few minutes at room temperature.Then, the oxidant TBHP (1.28 � 10�3 mol) was added and the re-action mixture was stirred for the desired time. The samples(0.005 L) were taken at certain time intervals. Each sample wasinjected at least twice in the GC, 1 mL each time. Formation ofproducts and consumption of substrates were monitored by GC.

3. Results and discussion

3.1. Synthesis and characterization

Scheme 1 shows a brief schematic for the synthesis of periph-erally tetra-substituted cobalt phthalocyanine complexes 6 and 7.The phthalonitrile derivatives 4 and 5 were synthesized from the1,3-bis(naphthalen-1-yloxy)propan-2-ol 1 and 1,3-bis(naphthalen-2-yloxy)propan-2-ol 2 by nucleophilic reaction with 4-nitrophthalonitrile 3 in the presence of K2CO3 and in dry DMF at 50 �C,respectively. After, in a microwave oven, cobalt phthalocyanines 6and 7 were obtained in the presence of metal salt (CoCl2) in DMAEat 175 �C, 350 Watt in average 6 min.

In the IR spectra, the formation of compounds 4 and 5 wasclearly confirmed by the disappearance of the OH and NO2 band atw3410 and w1538e1355 cm�1 and appearance of a single intensepeak (C<ce:glyph name¼"tbnd"/>N) at 2232 and 2231 cm�1,respectively. In the 1H NMR spectrum of 4 and 5, OH group ofcompounds 1 and 2 disappeared as expected. In the 1H NMRspectrum of compounds 4 and 5 the aromatic protons appear at8.08 (d), 7.84 (d), 7.66 (m), 6.89 (d) ppm for compound 4, 7.77 (m),7.53e7.18 (m) ppm for compound 5. Also nitrile carbon atoms wereobserved at 115.36, 112.57 ppm for compound 4, 115.61, 112.56 ppmfor compound 5. The MS spectrum of compounds 4 and 5, whichshows a peak atm/z ¼ 470 [M]þ supports the proposed formula forthese compounds.

The IR spectra of the cobalt(II) phthalocyanines 6 and 7 whichare very similar each other, show no the sharp C<ce:glyph

OH

O O

1 2

CN

CNO2N3

O

O O

CN

CN

5

OH

O O

O O

R1=

CN

CNO2N

4

OR1R1O

OR1R1O

N

N

N

N

N

NN

N

6

Co

OR2R2O

ORR2O

N

N

N

N

N

NN

N

7 2

Co

3i

i

ii

OO

O

O O

CN

CN

ii

R2=

Scheme 1. The synthetic phthalonitriles and cobalt phthalocyanine complexes. Reagents and conditions: (i) dry DMF, K2CO3, 60 �C; (ii) CoCl2, DMAE, 175 �C, 350 W.

A. Aktas et al. / Journal of Organometallic Chemistry 745-746 (2013) 18e2420

name¼"tbnd"/>N vibration peak (2232e2231 cm�1) which wasobserved in the IR spectra of 4 and 5. The 1H NMR spectra ofmetallophthalocyanines 6 and 7 could not be taken because of theparamagnetic cobalt(II) center. In the mass spectrum of Co phtha-locyanines, the presence of molecular ion peaks at m/z ¼ 1941[M þ H]þ, confirmed the proposed structures.

The UV/vis spectra of the cobalt(II) phthalocyanine complexes 6and 7 in DMF at room temperature are shown in Fig. 1. In UVevisspectra of the cobalt(II) phthalocyanines Q-bands were observed ataround 671 nm for 6, 669 nm for 7 with the shoulders at around

605 nm for 6, 604 nm for 7 and the B bands were observed between328 and 320 nm.

3.2. Catalytic studies

3.2.1. Oxidation of cyclohexene with complex 6 and complex 7Cyclohexene (0.77 � 10�3 mol), cobalt(II) phthalocyanine com-

plexes (2.57 � 10�6 mol), m-CPBA (1.28 � 10�3 mol) and DMF(0.01 L) were mixed in Schlenk vessel and refluxed at 90 �C with900 rpm stirring (Tables 1e4). The formed oxidized products were

Table 2Temperature effect of cyclohexene oxidation with complexes 6 and 7.

Catalyst T (�C) Alcohola Ketoneb Epoxidec Tot. conv. (%) TONd TOFe (h�1)

6 25 25 17 5 47 141 477 24 20 4 51 153 516 50 36 27 6 69 207 697 33 23 14 70 210 706 70 47 27 7 81 243 817 41 23 14 78 234 786 90 54 29 8 97 291 977 49 26 19 94 282 94

Conversion was determined by GC.Reacion time ¼ 3 h.

a 2-Cyclohexene-1-ol.b 2-Cyclohexene-1-one.c Cyclolohexene oxide.d TON ¼ mole of product/mole of catalyst (all products).e TOF ¼ mole of product/mole of catalyst � time(3 h).Fig. 1. UVevis spectrum of 6 and 7 in THF.

A. Aktas et al. / Journal of Organometallic Chemistry 745-746 (2013) 18e24 21

monitored with GC by spotting and comparing with standards.Blank experiments were done without the catalysts to observe vitalmission on the cyclohexene oxidaition. In Tables 1e4, differentoperation conditions were evaluated to compare the catalytic ac-tivity of 6 and 7. Then, the results show that for oxidation ofcyclohexene these complexes are active catalyst in DMF. Threetypes of oxidized product were obtained. They are 2-cyclohexene-1-ol as dominant product and 2-cyclohexen-1-one and cyclo-hexene epoxide (Fig. 2). To improve the conversion of cyclohexene,the parameters such as substrate/catalyst ratio, the reaction tem-perature, oxidant ratio and type of oxidants were investigated.

Surprisingly the conversion was reached the highest value after3 h when complexes 6 and 7were used as catalyst. But after 3 h, theconversion stayed the samevalue (Fig. 3a and b). Both catalystswereemployed as catalyst to give same oxidized product that is 2-cyclohexene-1-ol with high yield. Table 1 shows that cyclohexeneoxidation reactions were done with different the substrate/catalystratio (300e1500). The other reaction conditions are 1.28� 10�3molm-CPBA, 0.01 L DMF, 90 �C and 3 h. The low substrate catalyst molarratio done a remarkable acceleration effect on the reaction rate of

Table 1Amount of substrate effect of cyclohexene oxidation with complexes 6 and 7.

Catalyst Subs./cat. Alcohola Ketoneb

6 300/1 5429

7 4926

6 600/1 48 297 45 256 900/1 37

297 34

256 1200/1 30

227 27

186 1500/1 18

197 16

16

Conversion was determined by GC.Reacion time ¼ 3 h.

a 2-Cyclohexene-1-ol.b 2-Cyclohexene-1-one.c Cyclolohexene oxide.d TON ¼ mole of product/mole of catalyst (all products).e TOF ¼ mole of product/mole of catalyst � time(3 h).

cyclohexene oxidation. When the substrate concentration de-creases, the reaction rate increases. Looking at the data inTable 1 it iseasy to realize that 2-cyclohexene-1-ol as dominant product withselectivity of 54% and 49% for complexes 6 and 7 respectively.This study shows that the catalyst 6 and 7 with m-CPBA asoxidant leaned the formation of 2-cyclohexene-1-ol from the otherproducts.

Table 2 shows experimental results related to effect of tem-perature on cyclohexene conversion toward the products withox./subst./cat. ¼ 500/300/1 and m-CPBA, in DMF during 3 h. Forthis parameter, DMF was used as solvent due to its high boilingpoint. Whereby, we can study different temperature effect oncyclohexene oxidation. According to Table 2, we can concludethat the reaction temperature on the oxidation of cyclohexenewas raised when the catalytic activity of complexes 6 and 7increased. When the reaction temperature was increased to thehighest temperature, the yield of oxidized products wasincreased. The highest conversion at 90 �C was observed that 97%and 94% with TON ¼ 291 and 282 for complexes 6 and 7respectively. The overall conversion was increased 50% for

Epoxidec Tot. conv. (%) TONd TOFe (h�1)

8 97 291 97

19 94 282 94

8 85 510 17010 80 480 1608 74 666 222

10 69 621 207

5 57 684 228

6 51 612 204

3 40 630 210

4 36 540 180

O OH

OOxidant

Catalyst (MPc)

2-cyclohexene-1-ol2-cyclohexene-1-one cyclohexenoxideCyclohexene

Fig. 2. Product formed through oxidation of cyclohexene by TBHP, m-CPBA and H2O2

in the presence of complexes 6 and 7.

Table 3Different oxidant effect of cyclohexene oxidation with complexes 6 and 7.

Catalyst Oxidant Alcohola Ketoneb Epoxidec Tot.Conv.(%)

TONd TOFe

(h�1)

6 TBHP 33 26 6 65 195 657 34 23 10 67 201 676 H2O2 22 22 6 50 150 507 14 26 12 52 156 526 m-CPBA 54 29 8 97 291 977 49 26 19 94 282 9467

Freeoxidant

e e e e e e

Conversion was determined by GC.Reacion time ¼ 3 h.

a 2-Cyclohexene-1-ol.b 2-Cyclohexene-1-one.c Cyclolohexene oxide.d TON ¼ mole of product/mole of catalyst (all products).e TOF ¼ mole of product/mole of catalyst � time(3 h).

A. Aktas et al. / Journal of Organometallic Chemistry 745-746 (2013) 18e2422

complex 6 and 43% for complex 7, when the temperature wasraised 25e90 �C. The low reaction temperature did not favor theoxidation of cyclohexene. At the lowest temperature (25 �C),the conversion of cyclohexene to oxidized products only 47%for complex 6 and 51% for complex 7.

Table 3 shows that the data were obtained from the results ofoxidation experiments with different types of oxygen sources (suchas TBHP, m-CPBA, aerobic oxygen and H2O2). For these experi-ments, 1.28 � 10�3 mol m-CPBA, TBHP, H2O2 were used. Duringthese experiments, m-CPBA was found most effective oxidant onthe oxidation of cyclohxene with complexes 6 and 7 (Fig. 4). For theblank experiments, all reactions were done again without m-CPBAand we deduced that cyclohexene oxidation reactions did notprogress. The other oxygen sources like TBHP or hydrogen peroxidewere not found suitable oxidant for our catalytic system. The reasonof observation the lowest conversion with H2O2 is fast degradationof the phthalocyanine ring 6 and 7. The color of solution immedi-ately turned from the blue-green color of to colorless after addingH2O2. Because of this, complexes 6 and 7 were not employedeffectively as catalyst during the oxidation. When comparing theperformance of TBHP and H2O2, decomposition of phthalocyaninering of complexes 6 and 7 with THBP was lower than H2O2. Thehighest activity of complexes 6 and 7with m-CPBA (TOF:97 and 94)and other oxidant activity can be seen in Table 3.

Table 4 shows the results getting from cyclohexene oxidationreactionwith changinge substrate-to-oxidant ratio. This ratio effectwas worked in the range of 300/1e1200/1. When the ratio was

Table 4Amount of oxidant effect of cyclohexene oxidation with complexes 6 and 7.

Catalyst Oxidant/catalyst

Alcohola Ketoneb Epoxidec Tot. conv.(%)

TONd TOFe

(h�1)

6 300/1 40 22 7 69 207 697 22 19 16 57 156 526 500/1 54 29 8 97 291 977 49 26 19 94 282 946 700/1 49 25 8 82 246 827 38 24 17 79 237 796 1000/1 49 20 10 79 237 797 33 22 15 70 210 706 1200/1 34 19 9 62 186 627 22 20 14 56 168 56

Conversion was determined by GC.Reacion time ¼ 3 h.

a 2-Cyclohexene-1-ol.b 2-Cyclohexene-1-one.c Cyclolohexene oxide.d TON ¼ mole of product/mole of catalyst (all products).e TOF ¼ mole of product/mole of catalyst � time(3 h).

increased from 300 to 500, total conversionwas increased from%69to %97 for complex 6 and %57 to %94 for complex 7. But from thisratio until to 1200/1, the total conversion tended to decrease. Wecannot easily tell oxidant role at this stage, but this situation mayexplain as changing coordination of cobalt and iron ion and createnonactive species.

Table 5 barely demonstrate that the success of Co(II) phthalocy-anine catalysts 6 and 7 by comparison of themetallophthalocyanineand metalloporphyrin catalysts. We obtained the best reported re-sults in terms of TOF in literature for homogenous oxidation ofcyclohexene with m-CPBA in the presence of Co(II) phthalocyaninecatalysts.

3.3. Monitoring the oxidation system by UVevis spectroscopy

Within theUV spectrumof themetallophthalocyanines has beenobserved the existence of two absorption bands assigned to thetransition n / p* and p / p*. These absorbstion bands, that arecalled as B and Q bands, are observed in the UVevis spectra of Co(II)phthalocyanine complexes [28e39]. Also these bands are to befound in the spectra of the metallophthalocyanine complexes, but

Fig. 3. Time-dependent conversion of cyclohexene oxidation a) for catalyst 6 b) forcatalyst 7 [Reaction conditions: Cyclohexene (0.77 � 10�3 mol), cobalt(II) phthalocy-anine complexes (2.57 � 10�6 mol), m-CPBA (1.28 � 10�3 mol), DMF (0.01 L), 3 h and90 �C].

Fig. 5. Time-dependent changes in the visible spectrum of the oxidized complex 6observed on addition of TBHP (1.28 � 10�3 mol) to a reaction mixture containing0.77 � 10�3 mol cyclohexene and 2.57 � 10�6 mol complex 6 catalyst in 10 ml: (a)45 min; (d) 90 min; (c) 135 min (d) 180 min after addition of m-CPBA. All spectra forthe oxidized complex 6 were taken after sixfold dilution with DMF. (e) Visible spec-trum of (non-oxidized) complex 6.

Fig. 6. Time-dependent changes in the visible spectrum of the oxidized complex 7observed on addition of m-CPBA (1.28 � 10�3 mol) to a reaction mixture containing0.77 � 10�3 mol cyclohexene and 2.57 � 10�6 mol complex 7 catalyst in 10 ml: (a)45 min; (d) 90 min; (c) 135 min (d) 180 min after addition of m-CPBA. All spectra forthe oxidized complex 7 were taken after sixfold dilution with DMF. (e) Visible spec-trum of (non-oxidized) complex.

Fig. 4. The oxidant effect on cyclohexene oxidation [Reaction conditions: Cyclohexene(0.77 � 10�3 mol), cobalt(II) phthalocyanine complexes (2.57 � 10�6 mol), m-CPBA(1.28 � 10�3 mol), DMF (0.01 L), 3 h and 90 �C].

A. Aktas et al. / Journal of Organometallic Chemistry 745-746 (2013) 18e24 23

they broadens and shifts because of m-oxo dimeric species of Co(II)-Pc to Co(III)ePc [40]. Figs. 5 and 6 indicate spectral changesobserved for the catalysts 6 and 7 during the oxidation reactionwithm-CPBA. The typical monomeric form of Co(II) phthalocyaninecomplexes is seen in Fig. 1 before the start of the catalytic reactions.Q band at 669 nm for complexes 6 and 7 with respectively. Withadding of oxidant (such as TBHP, m-CPBA or H2O2), Q-band de-creases in intensity and broadens at 666 and 667 nm. Around the Bband religion (w480 nm) there is no peak. Thus addition of m-CPBAto solutions of Co(II) complexes resulted in only metal and not ringoxidation of Co-Pc. As catalysis proggressed, there was a prog-gressive decrease in the intensity of the Q band of the Co(II)phthalocyanine catalyst, suggesting catalyst degradation as istypical of MPc catalysts in homogenous catalysis [41]. The reason ofthis degradation can be explained as a result of the attack of thephthalocyanine ring by the alkoxy and alkylperoxide radicals whichare produced fromm-CPBA. It is noted the change of reaction colorthat from blue to green as catalysis continued. However, the reac-tion products continued to form even after the catalyst had turnedyellow, suggesting that once reaction intermediates are formed, thereaction can still progress in the presence or absence of the original

Table 5Catalytic activities toward the homogeneous oxidation of cyclohexene of somepreviously reported catalyst.

Catalyst Rxntime (h)

Rxntemp. (�C)

Oxidant Conv.(%)

Ref.

Co(tbpcH2a) 24 Rth O2 w45

w55w30

[42]

CoPcb 8 nri TBHP 45.3 [41]Co[NO]2 Cu[NOc]2 8 75 H2O2 27.6

43.50[43]

[Co(Me2salpnMe2d)] 8 40 TBHP 42.7 [44]Co(salen)ePOMCoPce

CoPcf

CoPcg

633

609090

H2O2

m-CPBAm-CPBA

91618045

[45][10][21]

a tbpcH2 ¼ tetra-tert-butylphthalocyanine.b Pc ¼ peripherally substituted phthalocyanine.c NO ¼ 2-pyrazinecarboxylic acid.d Me2salpnMe2 ¼ N,N-bis-(a-methylsalicylidene)-2,2-dimethylpropane-1.e Pc ¼ 4-{2-[3-(diethylamino)phenoxy]ethoxy} group substituted

phthalocyanine.f Pc ¼ 4-[2-(1,4-dioxa-8-azaspiro[4.5]dec-8-yl)ethoxy group substituted

phthalocyanine.g Pc ¼ 4-(3,3-diphenylpropoxy) group substituted phthalocyanine.h rt ¼ room temperature.i nr ¼ not reported.

form of the catalyst. Both phthalocyanine complexes were degra-gaded by the oxidant. These degradation were monitored changingcolor byUVevis spectroscopy.Whenweusedm-CPBAas an oxidant,the reaction color changed from blue to green and the oxidationprogressed, the catalyst turned yellow. This indicates that com-plexes 6 and 7 can exist a long time in reactionmedia and catalyzedeffectively without degradation on cyclohexene oxidation.

4. Conclusion

In conclusion, we have synthesized and characterized a newmetal free phthalocyanine, cobalt(II) complexes and showed theircatalytic activity in the selective oxidation of cyclohexene to 2-cyclohexen-one as dominant product, 2-cyclohexen-ol and cyclo-hexene oxide under homogenous conditions with TBHP in DMF.Wehave also investigated that UVevis spectrum of new cobalt(II)phthalocyanine complexes in different solvents (CH2Cl2, CHCl3, THFand DMF). The high percentage yield of reactions in the presence ofcobalt(II) phthalocyanine complexes seems promising.

Acknowledgments

This study was supported by the Research Fund of KaradenizTechnical University, Project no: 9666 (Trabzon-Turkey).

A. Aktas et al. / Journal of Organometallic Chemistry 745-746 (2013) 18e2424

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